1. Field of the Invention
This invention relates to a tolan derivative as a novel compound and a liquid crystal mixture containing the same.
2. Description of the Related Art
Display elements having applied liquid crystals utilize various electrooptical effects of liquid crystal substances, and the display mode thereof includes various modes such as twisted nematic mode, dynamic scattering mode, guest-host mode, DAP (Deformation of Vertically Aligned Phases) mode etc. The properties required for liquid crystal substances used for these modes vary depending on the respective modes, but it is required in common therewith that the liquid crystal substances exhibit liquid crystal phases within a temperature range as broad as possible and are stable to moisture, heat, air, etc. and also to light, electricity, etc. At present, however, no single substance which satisfies all of the above requirements exist, and currently that several kinds of liquid crystal compounds have been mixed or several kinds of liquid crystal compounds have been mixed with compounds similar to liquid crystal compounds and the resulting liquid crystal mixtures have been used.
As to examples of tolan derivatives used as a component of liquid crystal materials, compounds expressed by the following formulas (1) - (4) are respectively disclosed in (1) French patent application laid-open No. 2,141,438, (2) Japanese patent application laid-open No. Sho 60-152427/1985, (3) Japanese patent application laid-open No. Sho 61-260031/1986 and (4) Japanese patent application laid-open No. Sho 60-204731/1985: ##STR2## wherein R.sup.3 and R.sup.4 each represent an alkyl group or an alkoxy group, wherein ##STR3## represents ##STR4## and R.sup.5 and R.sup.6 each represent a linear alkyl group, ##STR5## wherein R.sup.7 represents a linear alkyl group and X represents a halogen atom, and ##STR6## wherein R.sup.8 and R.sup.9 each represent a linear alkyl group.
These tolan compounds are liquid crystal materials which exhibit a large optical anisotropy value (hereinafter referred to .DELTA.n) and a high clearing point.